Adverse responses to protamine sulfate have been known for many years. Previous exposure to protamine can induce a humoral immune response and predispose susceptible individuals to the development of untoward reactions from the subsequent use of this drug. Patients exposed to protamine through the use of protamine-containing insulin or during heparin neutralization may experience life-threatening reactions and fatal anaphylaxis upon receiving large doses of protamine intravenously. Severe reactions to intravenous protamine can occur in the absence of local or systemic allergic reactions to subcutaneous injection of protamine-containing insulin. Although there is no clear evidence for hypersensitivity reactions of protamine sulphate linked to vaccination, vaccines containing protamine impurities have a precaution and contraindication warning in their labels stating that a serious allergic reaction after a previous dose of such a protamine containing vaccine (e.g. IXIARO®, see CDC site www.cdc.gov/japaneseencephalitis/vaccine/) is a contraindication to further doses. Thus elimination of said impurity is a medical request for an improved safety profile. On the other hand protamine sulphate is an excellent tool (and often better than other tools such as benzonase) to purify crude harvests of viruses grown on cell substrates.
In 2007, Zika virus was detected for the first time outside of the endemic regions of Asia and Africa since its discovery in a Rhesus monkey in Uganda in 1947. Since then, the virus has caused a large epidemic in French Polynesia, spreading through islands in the Pacific and into South and Central America by 2015 (WHO “Zika Situation Report” Feb. 5, 2016). Evidence suggests that in addition to being transmitted by Aedes species mosquitoes, other vectors may exist, and the virus may be transmitted by blood transfusion, transplacentally, and through sexual transmission (WHO Zika Virus Fact Sheet, February 2016). Though the symptoms of Zika virus infection include mild fever, rash, and conjunctivitis, there is a likely correlation between infection and neurological disorders, including Guillain-Barré syndrome and microcephaly in fetuses/neonates subsequent to infection during pregnancy. There is currently no specific treatment or vaccine for Zika virus and the only preventative measures involve control of the mosquito vector. Zika virus presents a substantial public health threat due to the wide circulation of the Aedes mosquito, multiple routes of transmission, and potentially severe neurological effects of infection.
A preventative vaccine against Zika virus is a pressing medical need in endemic areas and in geographical areas where the vector is spreading. Furthermore, as Zika infection has dire consequences on embryonic and fetal development, a safe and effective vaccine for women of child-bearing potential or pregnant women is needed. Vaccines administered during pregnancy must be very safe for both the mother and the developing fetus. While live attenuated viral vaccines are highly effective, they are often not considered safe enough for administration to pregnant women. In this regard, inactivated viral vaccines, which lack the ability to propagate in the vaccinated subject, are considered much safer. Development of an inactivated Zika virus vaccine for administration to at-risk patients would fill this need.